Self-aligning track roller

ABSTRACT

A track-roller bearing assembly is disclosed which includes a fixed inner ball race member having an outwardly facing arcuate peripheral bearing surface; an annular body of self-lubricating bearing material affixed to the outwardly bearing surface of said inner race; and a coaxial outer race which is rotatable about an axis of the inner race and angularly displaceable relative to the axis of the inner race so as to accommodate track deflections or irregularities. The track-roller further includes a resilient element disposed between respective ends of the inner and outer races so as to bias the races back into axial alignment after they have been angularly displaced relative to each other.

This is a continuation-in-part of prior commonly owned application Ser.No. 567,612, filed Jan. 3, 1984, now U.S. Pat. No. 4,717,268, which wasa continuation of commonly owned Ser. No. 255,634 filed Apr. 20, 1981and now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a track roller and more particularly,to a self-aligning track roller for accommodation to variable tracksurfaces comprising a co-engaging inner race and outer race movablerelative to one another wherein an elastomeric element such as a ring isdisposed between respective ends of the inner and outer races so as tobias the inner race into alignment with the outer race. Further, theinner race has a bearing surface provided with a self-lubricatingmaterial which is engageable with and movable relative to the bearingsurface of the outer race.

At present, track rollers being used incorporate a crown radii on theouter diameter of the outer race to compensate for track deflections andirregularities. This reduces the contact area between the roller and themating surface of the track. An increase in contact bearing pressureresults due to the reduced contact area which has caused excessive wearand distress to the track surface.

Further, the conventional track roller bearings are constructed withrolling elements positioned between the inner and outer races andrequire a lubricant such as grease. Addition of lubricant to the rollingelements is periodically required to maintain the operationalperformance and to add corrosion resistance. Such bearings are subjectto failure where fracturing of the rolling elements and spalling of theinner race occur. In addition, the performance of these track rollerbearings depends on the effectiveness of seals incorporated thereinwhich ensure that the grease lubrication is maintained within thevarying surface area, proper, and that the grease lubrication is notcontaminated from external sources.

It is known to incorporate a self-lubricating liner system as analternative to the rolling element track roller surface of the outerrace so as to operate against the bearing surface of a hardened innerrace. These bearing assemblies have the advantage that they do notrequire periodic lubrication and they have a generally higher rollingload capacity. In addition, static radial load capacity of these bearingassemblies is substantially higher than the rolling element bearingassemblies with high thrust capacity being ensured by the use of theseparate self-lubricating liner system. These self-lubricating typebearing assemblies are discussed for example in U.S. Pat. Nos. 4,048,370and 4,134,842.

The self-lubricating liner systems with the liner attached to the innerdiameter of the outer race were designed in accordance with the beliefthat the wear experienced during the life of the bearing system could bedistributed over the full circumference of the liner and thus result inextended surface life. Nevertheless, it has been found that because ofthe rotation of the outer race liner in relation to the stationary innerrace and the unidirectional load application, liner systems with acompression modulus of up to about 1 million psi are subjected tomaterial deflection. More particularly, the mismatch of the inner racecircumferential surface to the outer race by differential tolerances andthe thickness of the liner system provide the mechanism which permitslocal deflection of the liner as the outer race moves relative to theinner race when loaded. Therefore, under a steady applied load, whilemoving in relation to the inner race, high shearing action and tensileforces are imposed on the liner immediately in front of the progressingload action of the inner race. This is known as ploughing. When combinedwith fluid contamination, the liner is further distressed due to thewedging action of fluid in front of the advancing inner race slider.

Lubricating material affixed to the outer race in a track-roller bearingassembly is subjected to distortion and consequent reduced service liferelative to the arrangement of the present invention. The induced linerdeflection when loaded by the inner race during rotation of the outerrace adversely affects the bond between the lubricating material and theouter race, and as the bond fails, the lubricating material is pinchedbetween the inner and outer races without any support and tends to besqueezed out.

SUMMARY OF THE INVENTION

The bearing assembly of the present invention overcomes theabove-mentioned problems associated with the provision of a drawn radiiby providing co-engaging inner- and outer races that are self-aligning.More particularly, in accordance with the present invention, anelastomeric element is provided about at least one and preferably bothends of the inner race adjacent a respective end of the outer race. Inthis manner, when relative angular rotation of the inner and outer racesdistorts the elastomeric element(s) the resiliency of the element(s)resists the deformation and urges the races into their original axialalignment.

The bearing assembly of the present invention also provides the linerbond failure occasioned by the above-described ploughing action andexhibits a significantly extended wear life. In the bearing assembly ofthe present invention the self-lubricating bearing material ispreferably provided on the outer bearing surface of the inner material.This construction ensures positive contact between the liner system andmating surfaces so that fluid contamination does not become a mechanicalwedging tool.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view illustrating a first embodiment of theself-adjusting, self-lubricating track roller of the present invention;

FIG. 2 is a sectional view illustrating a second embodiment of the trackroller of the present invention; and

FIG. 3 is a sectional view illustrating yet another embodiment of thepresent invention.

DETAILED DESCRIPTION

FIG. 1 is a sectional view of the improved bearing assembly of thepresent invention with the shaft omitted for clarity. As can be seen,the bearing assembly comprises an inner ball race 10 and an outer race12 engageable with and rotatable relative to inner ball race 10. In theillustrated embodiment outer race 12 includes first and second parts 14and 16. Further, outer race 12 has an inner arc surface defined by theinner portions of parts 14 and 16 that has a length less than thearcuate surface of inner race 10 so as to allow relative angularmovement of races 10 and 12 as will be described more fully below.

Inner race 10 of the illustrated embodiment includes a ball portion 18and first and second cylindrical portions 20. Cylindrical portions 20extend axially beyond an associated end face 22 of outer race 12.Further, the end faces 22 are inwardly inclined so as to be conical inshape and a gap 23 is provided between the cylindrical portions 20 andthe end faces 22 so that the inner and outer races 10 and 12 can beangularly displaced relative to one another to accommodate trackdeflections.

To provide the self-aligning characteristics of the bearing assembly, anelastomeric ring 24 is provided about at least one and preferably bothcylindrical portions 20 between same and an associated end face 22. Theelastomeric ring 24 so disposed is resiliently distorted when races 10and 12 are angularly displaced because of, for example, trackirregularities or other mechanical relations in a structure. However,the resiliency of ring 24 causes same to urge the races 10, 12 back intoaxial alignment and hence, the bearing assembly is self-aligning. As isfurther apparent, elastomeric ring(s) 24 also serve to cushion relativeangular movement so that, despite track deflections or irregularities,motion is more smoothly transmitted while stresses on the assembly areminimized.

Referring to FIG. 2, an alternate embodiment of a self-aligning rollerbearing is shown. In this embodiment, rather than wedge-shaped ring 24,realignment is provided by the combination of an O-ring 28 mounted on atleast one and preferably both end portions 20 and an elastomeric washer30 which is disposed between each O-ring 28 and its associated end face22. Of course an appropriatly sized O-ring formed of an appropriatematerial could be used in some circumstances without a washer 30.Further, the illustrated embodiment, a recess 32 is defined on thesurface of end portion 20 to receive O-ring 28 and retain the same inposition.

Turning to FIG. 3, yet another embodiment of the present invention isshown, on an inner race that is formed with only a single end portion34. In this embodiment, the self-aligning function is achieved throughthe combination of an elastomeric washer 36 disposed between an end face38 of the outer race 40 and a rigid wedge shaped ring 43 mounted to endportion 34 of inner race 44.

The elastomeric ring(s) 24 as well as O-ring(s) 28 and washer(s) 30, 36provided in accordance with the present invention of course may beformed from any suitable material but are preferably formed from, forexample, urethane, teflon, silicone, nitrile, neoprene or vyton and maybe adhesively secured in place as shown.

As can be further seen in FIGS. 1, 2 and 3, in the bearing assembly ofthe present invention, unlike the bearing assemblies of the prior art,the outer surface of inner race 10 is provided with a self-lubricatingbearing material 26 fixedly secured thereto. Bearing material 16 can befixed to the outer diameter of the inner race by any suitable means. Thebearing material 16 so affixed is engageable with and movable relativeto the inner surface of the outer race 12. Further, bearing material 16extends the entire arc length of the inner race 10 outer diameter sothat it will be disposed between outer race 12 and inner race 10 even atthe extremes of relative angular motion due to track deflections orirregularities.

Outer race 12 of the bearing assembly of the present invention is madeof metal, preferably stainless steel (wrought or powder metallurgy) suchas 440C, 13-8PH, AMS 5617-Custom 455, 17-4PH, 300 series, and morepreferably 13-8PH, although other metals such as high carbon steel 52100as well as case hardened titantium, anodized aluminum, Inconel,Hastelloy and A286 can also be employed, so as to provide a metal innerbearing surface.

Inner race 10 of the bearing assembly of the present invention can alsobe made of a metal such as defined above, and more preferably stainlesssteel 17-4PH. The outer surface thereof has fixedly secured thereto theself-lubricating material.

The self-lubricating material can be a solid organic lubricant such as asolid polyester, polyamide, polyphenylene sulfide, polyarylsulfone, apolyfluorocarbon or, a cured acrylate as disclosed in U.S. Pat. No.4,048,370 and incorporated herein by reference or even a woven fibermatrix impregnated, for example, with a cured acrylate composition asdisclosed in U.S. Pat. No. 4,134,842 also incorporated herein byreference or other resin systems. The self-lubricating material can besecured to the outer surface 29 of inner race by known methods.

Representative polyesters include aromatic polyesters Such asp-oxybenzoyl polyester which is commercially available, for instance,under the tradename Ekanol and sold by the Carborundum Co. Thispolyester material has a density ranging from 1.44-1.48 gcc and amelting point of about 800° F. Polyamides usefully employed in thepresent invention include, for instance, Nylon-6 and Nylon-6,6 althoughit will be recognized that other nylon formulations can also beemployed. Aromatic poly p-phenylene sulfides can also be employed andsuch polymers can have a molecular weight ranging as high as about13,000. They are available, commercially, under the tradename of Rytonby Phillips Petroleum Company, such a product having a specific gravityof about 1.34, a density of about 0.0485 lbs/in³ and a melting point ofabout 550° F. Polyfluorocarbons usefully employed in the presentinvention include polytetrafluoroethylene. Included in the polyarylsulfones suitable for use in the present invention are those which havea molecular weight ranging from about 30,000 to 60,000. One convenientpolyaryl sulfone is that sold commercially under the tradename Polymer360-3M Astrel 360 having a specific gravity of 1.36, a density of 0.049lbs/in³, a compressive strength at 73° F. of 17,900 psi and a meltingpoint of about 550° F. Polyimides employed in the present invention arearomatic polyimides which are available commercially under, forinstance, the tradenames 6f Vespel SP-1 (DuPont) which has a specificgravity ranging from about 1.41-1.43, a density of about 0.052 lbs/in³,a compressive strength at 73° F. of about 24,000 psi and a heatdistortion temperature at 264 psi of about 680° F. A modified VespelSP-1 polyimide is Vespel SP-21 which contains 15 weight percentgraphite, has a specific gravity of about 1.51, a density of about0.0546 lbs/in³ and a compressive strength at 73° F. of about 18,000 psi.Other polyimides include one available commercially as XPl-182 byAmerican Cyanamid which has a specific gravity of about 1.28, a densityof about 0.046 lbs/in³, a compressive strength at 73° F. of about 25,000psi and a heat distortion temperature at 264 psi of about 440° F. Stillanother polyimide commercially available is that sold under thetradename of Genom 3010 by General Electric and has a specific gravityof about 1.90, a density of about 0.068 lbs/in³, a compressive strengthat 73° F. of about 41,900 psi and a heat distortion temperature at 264psi of about 660° F. Polyimides containing polytetrafluoroethylene orgraphite fibers can also be used.

When the self-lubricating material selected is a cured mixture of anacrylate composition and a particulate solid lubricant, such aspolytetrafluoroethylene, the acrylate composition can be selected fromthe group consisting of

(a) a mixture of a major amount of a liquid acrylic ester selected fromthe group consisting of di-, tri-, and tetraesters of an acrylic acidand a polyhydric alcohol, a minor amount of a low molecular weightprepolymer of an ester of a low molecular weight alcohol having aterminal vinyl group and an aromatic polycarboxylic acid in solution insaid acrylic ester and an organic amide of the formula ##STR1## whereinR is selected from the group consisting of hydrogen and aliphatichydrocarbon of 1-20 carbon atoms in an amount sufficient to copolymerizesaid acrylic ester and prepolymer,

(b) a mixture of acrylic ester monomer, a peroxidic initiator in anamount sufficient to initiate polymerization of said monomer and anaminoalkoxyalkylamine of the formula R₁ --N(H)R₂ [OR₃ ]_(x) N(H)R₄wherein x is an integer of 1-6 inclusive, each of R₁ and R₄ is selectedfrom the group consisting of hydrogen and lower alkyl and each of R₂ andR₃ is a lower alkyl linking bridge between N and O, in an amountsufficient to accelerate the polymerization of said monomer,

(c) a mixture of an acrylic ester of an alkyl amino alkyl alcohol and aneffective amount of hydroperoxide catalyst, said acrylic ester havingthe formula ##STR2## wherein x is an integer of 0-5 inclusive, y is aninteger of 1-6 inclusive, R is selected from the group consisting ofhydrogen, halogen, hydroxy, cyano and lower alkyl and R₁ is selectedfrom the group consisting of hydrogen and alkyl having 1-6 carbon atoms,

(d) a mixture of a liquid acrylic ester monomer selected from the groupconsisting of diesters of an acrylic acid and a polyhydric alcohol,acrylic esters of cyclic ether alcohols, acrylic esters of aminoalcohols and mixtures thereof, a peroxidic initiator and anoxyalkylamine of the formula (H)_(m) N[(CH₂)_(x) (OR₁)_(y) OR₂ ]_(n)wherein m and n are each integers of 1 to 2 inclusive, the total of mand n is 3, x is an integer of 1 to 6 inclusive, y is an integer of 0 to6 inclusive, R₁ is lower alkyl and R₂ is selected from hydrogen andlower alkyl,

(e) a mixture of an acrylic ester monomer selected from the groupconsisting of di-, tri- and tetraesters of an acrylic acid and apolyhydric alcohol, acrylic esters of cyclic ether alcohols, acrylicesters of amino alcohols and mixtures thereof, a peroxidic initiator ofan amount sufficient to initiate polymerization of said monomer and amember selected from the group consisting of rhodanine and a hydrazideof the formula ##STR3## wherein R and R' are selected from separategroups and an interconnected group forming a cyclic ring, R is furtherselected from the group consisting of hydrogen, alkyl, cycloalkyl, aryland alkoxy and R' is selected from the group consisting of hydrogen,alkyl, cycloalkyl, acyl and dithiocarbonyl in an amount sufficient toaccelerate the polymerization of said monomer; and

(f) a mixture of a monomer of the formula ##STR4## wherein R₁ and R areselected from the group consisting of hydrogen and lower alkyl and R isselected from the group consisting of lower alkyl, lower hydroxyalkyl,cyano and lower cyanoalkyl; at least one equivalent of an acid for eachequivalent of said monomer, said acid being selected from the groupconsisting of acrylic acid and lower alkyl acrylic acids; an initiatorselected from the group consisting of t-butyl perbenzoate, t-butylperacetate and di-t-butyl diperphthalate, said initiator being presentin an amount sufficient to initiate the polymerization of said monomer;a trihydroxy benzene inhibitor and an accelerator selected from thegroup consisting of benzhydrazide and N-aminorhodanine.

When the self-lubricating material selected is a woven fiber matriximpregnated with a cured acrylate composition, the woven fiber matrixcan comprise a material woven from a mixture of fibers, one face of thematerial comprising lubricating fibers, the other comprising reinforcingfibers. Conveniently the woven fiber matrix can be fabricated frompolytetrafluoroethylene fibers, as the lubricating fibers; and from suchreinforcing fibers as KEVLAR fibers, polyethylene terephthalate (DACRON)fibers as well as fiberglass and graphite fibers. Preferably, thereinforcing fibers are KEVLAR fibers, available commercially under thetradename KEVLAR PRD 49, by DuPont. KEVLAR is an organic polymericcompound known as an aromatic polyamide, i.e. an aramid. It is a highstrength, high modulus fiber made from long chain synthetic polyamideswherein at least 85 percent of the amide linkages are attached directlyto two aromatic rings. KEVLAR fiber is extremely stable, has highstrength, toughness and stiffness characteristics. The density of KEVLARPRD 49 is 1.45 g/cc and its mechanical properties lie between the valuesof glass and graphite filament. The curable acrylate, which can be anyof those defined above at (a) through (f) is present in an amountsufficient to impregnate the woven fiber matrix and to bond the same tothe outer surface of the inner race.

As is apparent from the foregoing, to compensate for track deflectionsand irregularities, the track roller of the present invention isself-adjusting in that the outer race can rotate angularly relative tothe axis of the inner race in response to the variable track surface.This maintains the contact area between the rolling and the matingsurface of the track so that the contact bearing pressure will not beincreased and excessive wear and distress of the track surface isminimized. Further, the track roller of the present invention isself-aligning in that the inner and outer races are urged back intoaxial alignment when the races have been so angularly displaced.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A track-roller bearing assembly comprising:aninner ball race member having a central axis and an outwardly facingarcuate peripheral bearing surface, said inner race member including acylindrical portion extending outwardly along said central axis fromeach end thereof; an outer race member coaxial with said central axis ofsaid inner race member and including a bearing portion having an annulararcuate surface, said outer race member having inwardly tapered conicalend faces, said outer race member being rotatable about said centralaxis of said inner race member and angularly displacable relative tosaid axis; and means for realigning said central axis of said outer racemember with said central axis of said inner race member when said racemembers have rotated angularly relative to each other, said realigningmeans being disposed between each said cylindrical portion and arespective conical end face of said outer race member.
 2. A track-rollerbearing assembly as in claim 1, wherein said realigning means comprisesfirst and second wedge-shaped annular resilient ring members, a ringmember being disposed at each end of the bearing assembly.
 3. Atrack-roller bearing assembly as in claim 2, and further comprising anannular body of self-lubricating bearing material affixed to theoutwardly facing bearing surface of said inner race member; said bearingportion of said outer race member being in sliding engagement with saidbearing material.
 4. A track-roller bearing assembly as in claim 1,wherein said realigning means comprises at least one of an O-ring and anelastomeric washer member disposed at each end of the bearing assembly.5. A track-roller bearing assembly as in claim 4, and further comprisingan annular body of self-lubricating bearing material affixed to theoutwardly facing bearing surface of said inner race member; said bearingportion of said outer race member being in sliding engagement with saidbearing material.